If:

• a cache is specified for QNetworkAccessManager and

• PreferCache is specified using QNetworkRequest's method setAttribute called like
  setAttribute(QNetworkRequest::CacheLoadControlAttribute, QNetworkRequest::PreferCache) and

• the network/internet connection is not present

then, the request will still fail when called from a RichText QML Text with

QML QQuickText: Network access is disabled.

However, if you modify the setAttribute call to use QNetworkRequest::AlwaysCache when the network isn't present, then it will work:

cacheRequest.setAttribute(QNetworkRequest::CacheLoadControlAttribute,
    (networkAccessible() == QNetworkAccessManager::Accessible ?
        QNetworkRequest::PreferCache :
        QNetworkRequest::AlwaysCache));

I would like to suggest that this is a bug, because if you say you would PreferCache, you don't want it to fail if you have a valid cache entry, but the network isn't present.

For more code context, see this StackOverflow answer by jpnurmi